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In recent years, the blue orchard bee (BOB) has become established as an alternative orchard pollinator in North America. With a strong preference for fruit trees, BOBs are highly efficient pollinators; in fact, just 250-300 females will pollinate an entire acre of apples or cherries. BOBs forage and pollinate under cloudy skies and at lower temperatures than most other bees. They are easy to manage and rarely sting.

BOBs are solitary nesting bees

They nest in 5/16" diameter holes, 6" deep

When properly managed, they can provide excellent pollination on their own or with honey bees

Cherries being harvested from an orchard pollinated by blue orchard bees.

How To Distinguish Blue Orchard Bee Nests From Those Of Other Wild Bees

The blue orchard bee (BOB), Osmia lignaria, is increasingly sought by people who are commercially trap-nesting wild bees in the western USA. Dozens of other native bees, including other Osmia species, may be inadvertently obtained, particularly if the nest tubes are left out during the summer. Timely pick-up by late spring will avoid many of these unwanted species, especially prevalent summer bees such as Megachile.

When recovering blocks/reeds/tubes from the field, initially all one sees are the end caps of the nests, which for some species may be recessed. With practice and a hand lens, the probable identity of the nest can be learned from the nature of the cap itself, or certainly what the occupant is not, based on the material(s) constituting the cap and its surface texture. Most species of cavity-nesting Osmia make closures from leaf pulp (mastic), including the earliest spring nester, Osmia ribifloris .

It is ultimately important to sort by-catch from BOB, both for quality control and also to avoid shipping other species out of their native ranges The by-catch should be returned to the wild, but several hundred yards from where nest blocks will be placed the following year.

Below is a visual guide to some of the common or more recognizable nest caps one is likely to encounter when trap-nesting BOBs, particularly in northern Utah.

These bees do have their own pests and diseases, however, nest materials and management techniques are available to deter or remove many of these from the bees nesting in an orchard.

Examples of pests include:

Beetle Predators

The adult checkered flower beetle (Trichodes ornatus) is very colorful, and females lay their eggs in bee nests. The larvae prey on the developing bee brood, and eat the pollen provisions. The larvae have a somewhat worm-like appearance and a red color.

Blister beetles (Tricrania stansburyi) lay their eggs in flowers, and when the eggs hatch, the new larvae wait for a bee to come and visit, then hop a ride to the bee's nest. In this way, the beetle larvae finds its way into a sealed nest cell, where it kills the bee egg and feeds on the pollen provision. Only one blister beetle develops in one bee cell.

Flour beetles (Tribolium spp.) lay their eggs in the nests, and the larvae feed on the pollen provisions. They typically do not harm the bees directly.

Carpet beetles, such as this larva, commonly scavenge in bee nests. Carpet beetles belong to the Family Dermestidae.

Some wasps are parasites of the developing bee larvae. Typically the tiny female wasp enters the nest through cracks and crevices, then locates a developing bee larvae and lays her eggs. Infested cells can be identified by a large number of very small larvae in a cell, rather than the typical single large larva per cell of the blue orchard bee. Assuring that the backs of the nest cavities are sealed tightly, such that the wasps cannot enter through the back of the straw, will help reduce parasite infestations. Some of the parasites include the Chalcidae wasps:

Leucospis

Monodontomeris

And the beautiful metallic green Chrysididae wasp, Chrysura

Other parasites lay their eggs in the nests, and are called "cleptoparasites." Cleptoparasites kill the immature blue orchard bee and eat all their food. Sometimes other solitary bees can be cleptoparasites, too.

Sapyga are cleptoparasitic wasps of the blue orchard bee.

Stelis is a bee that is a cleptoparasite. It is also called the cuckoo bee. Its looks are similar to the blue orchard bee, but it is smaller, and the fecal pellets are long and curly, allowing one to identify it in the nest.

Pollen mites, also called hairy fingered mites (Chaetodactylus krombeini) can also be cleptoparasites. Heavy infestations can starve out the developing brood. The mites cannot move between the mud partitions in a nest, unless the partition is damaged during when the nests are moved.

Pollen mites infesting a blue orchard bee cell.

Chalkbrood. Very little is known about the diseases of blue orchard bees, but the most common disease is chalkbrood, caused by fungi in the genus Ascosphaera. The biology of chalkbrood in the blue orchard bee is very similar to chalkbrood in the alfalfa leafcutting bee.

Chalkbrood-infected brood

Using Blue Orchard Bees on Almonds:

The cost of renting honey bee hives for almond pollination service was about $50 per hive in 2003, but in 2009, the cost had increased to about $150-170 per hive. Between 2003 and 2005, the hive rental costs increased three-fold. This increase was due to a shortage of bees caused, on one hand, by declines in honey bee colonies due to varroa mites and colony disorder, and on the other hand, to rapid increases in almond acreage. The price of honey bee colonies is expected to level off at current prices as the markets come into balance.

California's 2005 almond acreage was estimated at 680,000 acres, a 6 percent increase from 2004's acreage of 640,000. Bearing acreage is forecasted to be over 800,000 by 2012 (USDA, National Agricultural Statistics Service). Almond growers typically use 2-3 colonies per acre, and at this rate, they require about 65% of all the honey bee colonies currently on record in the U.S.!

Blue Orchard bees are a good supplement or alternative to honey bees for almond pollinations. They are becoming commercially available for almond producers, although currently on a smaller scale than honey bees. Our laboratory has been working on developing blue orchard bee pollination systems for 20 years.

Using Blue Orchard Bees on other orchard crops:

While the cost of honey bee hives for other orchard crops is not as high as for almond, blue orchard bees are still a good supplement and help diversify the pollinator pool for these crops as well.

Almond, cherry, pear, and apple trees have a brief flowering period and flowers are receptive only for a few days; BOBs have a brief nesting period. Only a few are needed per acre (~1000-1500 bees, or ~300 nesting females).

Cool temperatures slow pollen germination; Female BOBs land on top of flower sexual columns and they strongly prefer flowering trees, so appropriate pollen is available on stigmatic surface to begin growth as soon as temperatures allow.

Cross pollination is required in all fruit trees, so bees must move between different cultivars; BOB females visit many trees in a short time and readily move between rows of trees.

Management of the Blue Orchard Bee (BOB) is quite different than for honey bees. BOBs have one generation per year and each female has her own nest.

The commercially available bees (still in cocoons) need to be adults for 30 days before cooling (Fall). Then at least 180 days at or below 45 oF (Winter) in order to emerge 1-7 days after warming (72-78 oF)(Spring).

Nesting Material

Nest material should: have holes about 5/16" in diameter (ideally, 19/64"); be about 6" long; be 3/4" apart (although, if hole entrances are offset, they can be closer); be plugged at the back to seal against light and parasites; be thick enough to block light and parasitism by wasps; should be lightweight and economical (although avoid plastic, it leads to mold); placed close to release site. For more information on building a nesting board, view our instructions.

Shelters

Shelters should: be open; face Southeast; provide protection from direct mid-day sunlight; be protected from rain; provide some morning solar warming in areas where temperatures are marginal for bloom and flight; ideally be spaced at 1 per acre; be large enough to provide 2-4 holes per female released; ideally be placed within orchard (in years of limited flight time, shorter flight distance restricts pollination to nearby trees); be small enough to be out of the way of spray rigs.

More Information

Further information on using BOBs can be found in our 2001 publication "How to manage the blue orchard bee as an orchard pollinator." This book is currently out of print, but available in pdf format.